Exhaust gas purifying apparatus for internal combustion engine

ABSTRACT

An exhaust gas purifying apparatus for an internal combustion engine, having a filter for trapping particulates in exhaust gases from the engine, is disclosed. A first particulate amount indicates an amount of particulates to be trapped by the filter and is calculated according to an operating condition of the engine. A second particulate amount indicates an amount of particulates trapped by the filter and is calculated according to a temperature of the filter when a filter regeneration of burning the particulates trapped by the filter is performed. The first particulate amount is compared with the second particulate amount, and a failure determination of the filter is performed according to a result of the comparison.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas purifying apparatus for an internal-combustion engine, and particularly, to the exhaust gas purifying apparatus having a filter (DPF: Diesel Particulate Filter) for trapping particulates (particulate matter) in exhaust gases of the internal combustion engine.

2. Description of the Related Art

A technique of providing a DPF which traps particulates in exhaust gases in the exhaust system of a diesel internal combustion engine and reduces an emission amount of particulates is conventionally and widely used. If a failure, such as a crack or a hole, occurs in the filter element of the DPF, the filtering capability of the DPF deteriorates and the emission amount of particulates increases. Therefore, it is necessary to quickly detect such failure.

Japanese Patent Laid-open No. 2004-308454 shows a method of providing a pressure sensor on the downstream side of the DPF, calculating a difference between the maximum value and the minimum value, i.e., a pulsation amplitude, of the detected pressure during engine operation, and determining that a failure occurs when the calculated pulsation amplitude is outside of a predetermined range.

According to the technique shown in Japanese Patent Laid-open No. 2004-308454, a leak amount of particulates due to the failure cannot be detected. Therefore, it is difficult to satisfy the demand of detecting a failure before the leak amount of particulates exceeds a predetermined amount due to reduction in the particulate trapping capacity of the DPF. Further, according to the technique shown in Japanese Patent Laid-open No. 2004-308454, complicated calculations are necessary for monitoring and analyzing the pulsation amplitude of the exhaust pressure.

SUMMARY OF THE INVENTION

The present invention was attained in view of the above-described points. An aspect of the present invention is to provide an exhaust gas purifying apparatus which can accurately detect a state of a failure of the DPF with a comparatively simple configuration.

In order to attain the above aspect, the present invention provides an exhaust gas purifying apparatus for an internal combustion engine (1) having filtering means (12) for trapping particulates in exhaust gases from the engine (1). The exhaust gas purifying apparatus includes first trapping amount calculating means, second trapping amount calculating means, and failure determining means. The first trapping amount calculating means calculates a first particulate amount (GDPF1) indicative of an amount of particulates which are to be trapped by the filtering means (12), according to an operating condition of the engine. The second trapping amount calculating means calculates a second particulate amount (GDPF2) indicative of an amount of particulates which are trapped by the filtering means (12), according to a temperature (TDPF) of the filtering means (12) when a filter regeneration of burning the particulates trapped by the filtering means is performed. The failure determining means compares the first particulate amount (GDPF1) with the second particulate amount (GDPF2), and performs a failure determination of the filtering means according to a result of the comparison.

With this configuration, the first particulate amount indicative of the amount of particulates to be trapped by the filtering means is calculated according to the temperature of the filtering means. The second particulate amount indicative of the amount of particulates trapped by the filtering means is calculated according to the temperature of the filtering means when the filter regeneration of burning the particulates trapped by the filtering means is performed. The failure determination of the filtering means is performed according to the comparison result which is obtained by comparing the first particulate amount with the second particulate amount. An amount of change in the temperature of the filtering means during the filter regeneration is substantially proportional to the amount of trapped particulates. Therefore, the second particulate amount, which is indicative of the amount of particulates trapped by the filtering means, is calculated according to the temperature of the filtering means.

On the other hand, the first particulate amount calculated according to the engine operating condition indicates an amount of particulates emitted from the engine. Accordingly, a crack or a hole is considered to be present in the filtering means if the difference between the first and second particulate amounts is significant. Therefore, a failure of the filtering means is accurately determined by comparing the first and second particulate amounts.

Preferably, the failure determining means calculates a particulate trapping rate (PMCE) of the filtering means (12) according to a ratio (GDPF2/GDPF1) of the first and second particulate amounts, and determines that the filtering means (12) fails when the particulate trapping rate (PMCE) is less than or equal to a predetermined threshold value (CETH).

With this configuration, the particulate trapping rate of the filtering means is calculated according to the ratio of the first and second particulate amounts, and it is determined that the filtering means fails when the particulate trapping rate is less than or equal to the predetermined threshold value. As described above, the first particulate amount indicates the amount of particulates emitted from the engine, and the second particulate amount indicates the amount of particulates actually trapped by the filtering means. Therefore, a ratio of the second particulate amount to the first particulate amount corresponds to the particulate trapping rate of the filtering means. Consequently, the fact that the particulate trapping rate is less than or equal to the predetermined threshold value indicates that the trapping of particulates by the filtering means fails to be performed normally, and then it can be determined that the filtering means fails. By calculating the particulate trapping rate of the filtering means, it becomes possible to determine a degree of the failure (whether the failure is serious or slight).

Preferably, the first trapping amount calculating means calculates the first particulate amount (GDPF1) by calculating an emission amount of particulates from the engine at constant time intervals according to the operating condition of the engine, and accumulating the emission amount.

Preferably, the filter regeneration is performed by a post-injection for increasing an amount of fuel supplied to the engine, or naturally performed in a high load operating condition of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of an internal combustion engine having an exhaust gas purifying apparatus and a control system therefor according to a preferred embodiment of the present invention;

FIG. 2 is a flowchart illustrating a process of the failure diagnosis;

FIG. 3 illustrates a table which is used in the process of FIG. 2; and

FIG. 4 illustrates an alternate embodiment of the process of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine having an exhaust gas purifying apparatus and a control system therefor according to one embodiment of the present invention. The internal combustion engine 1 (hereinafter referred to as “engine”) is a diesel engine wherein fuel is injected directly into the cylinders. Each cylinder is provided with a fuel injection valve 16 that is electrically connected to an electronic control unit 20 (hereinafter referred to as “ECU 20”). The ECU 20 controls a valve opening period and a valve opening timing of each fuel injection valve 16.

The engine 1 has an intake pipe 2, an exhaust pipe 4, and a turbocharger 8. The turbocharger 8 includes a turbine 10 and a compressor 9. The turbine 10 is driven by the kinetic energy of exhaust gases. The compressor 9, which is rotationally driven by the turbine 10, compresses the intake air of the engine 1.

The turbine 10 has a plurality of movable vanes (not shown), and is configured so that the rotational speed of the turbine 10 is adjusted by changing an opening of the movable vanes (hereinafter referred to as “vane opening”). The vane opening of the turbine 10 is electro-magnetically controlled by the ECU 20.

The intake pipe 2 is provided with an intercooler 5 and an intake shutter 3 (throttle valve)-on the downstream side of the compressor 9. The intercooler 5 cools pressurized air. The intake shutter 3 controls an intake air amount and the opening and closing of the intake shutter 3 is controlled by the ECU 20.

An exhaust gas recirculation passage 6 is provided between the upstream side of the turbine 10 in the exhaust pipe 4 and the downstream side of the intake shutter 5 in the intake pipe 2. The exhaust gas recirculation passage 6 is provided with an exhaust gas recirculation control valve 7 (hereinafter referred to as “EGR valve”) that controls the amount of exhaust gas that is recirculated. The EGR valve 7 is an electromagnetic valve having a solenoid. A valve opening of the EGR valve 7 is controlled by the ECU 20.

The exhaust pipe 4 is provided with a catalytic converter 11 and a DPF 12 in this order along the exhaust gas flow. The catalytic converter 11 and the DPF 12 are disposed downstream of the turbine 10.

The catalytic converter 11 has a NOx absorbent for absorbing NOx and a catalyst for promoting oxidization and reduction of the inflowing gases. The NOx absorbent absorbs NOx in the exhaust lean condition where the air-fuel ratio of the air-fuel mixture in the combustion chamber of the engine 1 is set in a lean region with respect to the stoichiometric ratio, and the oxygen concentration in the exhaust gases is therefore relatively high (the proportion of NOx is large). The NOx absorbent discharges the absorbed NOx in the exhaust rich condition where the air-fuel ratio of the air-fuel mixture is set in the vicinity of the stoichiometric ratio or in a rich region with respect to the stoichiometric ratio. Therefore, the oxygen concentration in the exhaust gases is relatively low.

The catalytic converter 11 is configured wherein the NOx discharged from the NOx absorbent is reduced by HC and CO in the exhaust rich condition and emitted as nitrogen gas, and the HC and CO are oxidized into water vapor and carbon dioxide.

When the exhaust gases pass through small holes in the filter wall, the DPF 12 traps soot, which consists of particulates in the exhaust gases whose main component is carbon (C). Specifically, the inflowing soot is accumulated on the surface of the filter wall and in the small holes in the filter wall. For example, ceramics such as silicon carbide (SiC) or porous metal are used as materials for the filter wall.

If the DPF 12 traps soot up to the upper limit of the soot trapping capacity, i.e., to the accumulation limit, the exhaust pressure rises excessively. Therefore, it is necessary to perform the regeneration process for burning the trapped soot before the amount of trapped soot reaches the accumulation limit. In the regeneration process, the post-injection control is performed for raising the temperature of exhaust gases to the burning temperature of soot. In the post-injection control, the post-injection is performed during the explosion stroke or the exhaust stroke after the compression stroke, in addition to the normal injection during the compression stroke. The fuel injected in the post-injection burns in the combustion chamber of the engine 1 or in the catalytic converter 11, depending on the fuel injection timing.

The DPF12 is provided with a DPF temperature sensor 23 for detecting a temperature (hereinafter referred to as “DPF temperature”). The detection signal of the temperature sensor 23 is supplied to the ECU 20.

Further, a crank angle position sensor 22 for detecting a rotation angle of the crankshaft of the engine 1, an intake air flow rate sensor 21 for detecting an intake air flow rate GA of the engine 1, a cooling water temperature sensor (not shown) for detecting a cooling water temperature of the engine 1, and the like, are provided. The detection signals of these sensors are supplied to the ECU 20. The rotational speed NE of the engine 1 is calculated from the output of the crank angle position sensor 22.

The ECU 20 includes an input circuit, a central processing unit (hereinafter referred to as “CPU”), a memory circuit, and an output circuit. The input circuit has various functions, including shaping the waveform of input signals from various sensors, correcting a voltage level to a predetermined level, and converting analog signal values into digital signal values. The memory circuit stores operation programs to be executed by the CPU, results of the calculations performed by the CPU, and the like. The output circuit supplies driving signals to the fuel injection valve 16 and the EGR valve 7.

FIG. 2 is a flowchart showing a method of determining a failure of the DPF 12. Specifically, deterioration of the filtering capability due to a crack or a hole in the filter wall is determined. The failure determination process is executed by the CPU in the ECU 20.

In step S101, an amount GDPF1 (hereinafter referred to as “first DPF accumulation amount”) of the particulates to be trapped by the DPF12 is calculated. The calculation of the first DPF accumulation amount GDPF1 is performed by a known method, such as calculating an emission amount of particulates from the engine 1 at constant time intervals based on the algorithm and a previously stored map according to the engine operating condition (e.g., the engine rotational speed NE and the intake air flow rate GA), and accumulating the calculated emission amount. Specifically, the first DPF accumulation amount GDPF1 indicates an accumulation amount when all of the particulates emitted from the engine 1 are trapped by the DPF 12. Therefore, the actual accumulation amount takes a value which is less than the first DPF accumulation amount GDPF1 when a crack or a hole is present in the filter wall of the DPF 12.

In step S102, it is determined whether the regeneration control for burning the accumulated soot is performed. If the first DPF accumulation amount GDPF1 calculated in step S101 does not exceed a predetermined regeneration control threshold value GPTH, the answer to step S102 becomes negative (NO), and the failure determination is not performed. If the first DPF accumulation amount GDPF1 exceeds the predetermined regeneration control threshold value GPTH, the regeneration control is performed, and step S103 and the following steps are executed. The regeneration control is performed post-injection to raise the exhaust gas temperature as described above.

In step S103, the DPF temperature TDPF is measured with the DPF temperature sensor 23. The DPF temperature TDPF is the maximum value of the temperature measured when performing the regeneration control. In step S104, a GDPF2 table shown in FIG. 3 is retrieved according to the DPF temperature TDPF to calculate an amount of particulates trapped in the DPF 12 (hereinafter referred to as “second DPF accumulation amount”). The GDPF2 table is set wherein the second DPF accumulation amount GDPF2 increases as the DPF temperature TDPF rises. The DPF2 table is previously stored in the memory circuit in the ECU 20 by measuring the relationship between the DPF temperature TDPF and the amount of trapped particulates with the understanding that the DPF temperature TDPF becomes higher as the amount of particulates which burn during regeneration control increases.

In step S105, the first DPF accumulation amount GDPF1 and the second DPF accumulation amount GDPF2 are applied to the following equation (1), to calculate a trapping rate PMCE of particulates by the DPF 12. PMCE=GDPF2/GDPF1  (1)

In step S106, it is determined whether the trapping rate PMCE is less than or equal to a determination threshold value CETH (for example, 0.8). If the trapping rate PMCE is less than or equal to the determination threshold value CETH, it is determined that the DPF 12 fails, i.e., the filtering capability of the DPF 12 deteriorates due to a crack or a hole in the filter wall (step S107). If the trapping rate PMCE is greater than the determination threshold value CETH, the DPF 12 is determined to be normal (step S108).

As described above, in this embodiment, the first DPF accumulation amount GDPF1, which is indicative of the amount of particulates which should be trapped in the DPF 12, is calculated according to the operating condition of the engine 1. The second DPF accumulation amount GDPF2, which is indicative of the amount of particulates actually trapped in the DPF 12, is calculated according to the DPF temperature TDPF measured when the regeneration control of the DPF 12 is performed. Failure determination of the DPF 12 is performed according to a result that is obtained after comparing the first accumulation amount GDPF1 and the second accumulation amount GDPF2. The first DPF accumulation amount GDPF1, calculated according to the engine operating condition, indicates an amount of particulates emitted from the engine 1. Accordingly, a crack or a hole is considered to be present in the DPF 12 if the difference between the first and second particulate amounts is significant. Therefore, a failure of the DPF 12 can accurately be determined by comparing the first and second particulate amounts GDPF1 and GPDF2.

More specifically, the trapping rate PMCE is calculated as a ratio of the second DPF accumulation amount GDPF2 to the first DPF accumulation amount GDPF1. It is determined that the DPF 12 fails if the trapping rate PMCE is less than or equal to the determination threshold value CETH. By calculating the trapping rate PMCE, it is possible to determine a degree of the failure (whether the failure is serious or slight) of the DPF 12.

In this embodiment, the DPF 12 corresponds to the filtering means. The intake air flow rate sensor 21, the crank angle position sensor 22, and the ECU 20 represent the first trapping amount calculating means. The temperature sensor 23 and the ECU 20 represent the second trapping amount calculating means. The ECU 20 represents the failure determining means. Specifically, step S101 of FIG. 2 corresponds to the first trapping amount calculating means. Steps S103 and S104 correspond to the second trapping amount calculating means. Steps S105-S108 correspond to the failure determining means.

In the embodiment described above, the failure diagnosis is performed during the regeneration control of the DPF 12 with the post injection. Alternatively, in another or second embodiment, the failure diagnosis is performed while regeneration of the DPF 12 is performed naturally, for example, in the high load engine operation. In the high load engine operation, the temperature of the exhaust gases rises and the natural regeneration, wherein the particulates trapped in the DPF 12 naturally burn, is performed. Accordingly, in such an engine operating condition, the failure diagnosis is performed without performing the regeneration control.

FIG. 4 is a flowchart showing a method of the failure diagnosis in the second embodiment of the present invention. The flowchart shown in FIG. 4 is obtained by changing step S102 of FIG. 2 to step S102 a. In step S102 a, it is determined whether the natural regeneration is performed. Step S102 and the following steps are executed when the natural regeneration is performed. For example, it is determined that the natural regeneration is performed when both the engine rotational speed and the engine load exceed corresponding predetermined threshold values.

Further, in the embodiment described above, the trapping rate PMCE is calculated and the failure determination is performed by comparing the trapping rate PMCE with the determination threshold value CETH. Alternatively, it may be determined that the DPF 12 fails if the difference between the first DPF accumulation amount GDPF1 and the second DPF accumulation amount GDPF2 is greater than a corresponding determination threshold value.

Further, in the embodiment described above, the temperature sensor 23 directly detects the temperature of the DPF 12 during regeneration control. Alternatively, a temperature sensor may be disposed downstream of the DPF 12, and a temperature TDEX of the exhaust gases from the DPF 12 may be detected as the temperature of the DPF 12. Further, a temperature TDIN on the upstream side of the DPF 12 may be detected, a temperature rise amount ΔTDPF may be calculated by subtracting the upstream temperature TDIN from the downstream temperature TDEX, and the second DPF accumulation amount GDPF2 may be calculated according to the temperature rise amount ΔTDPF.

Further, a temperature accumulated value ITDEX may be calculated by detecting and accumulating the downstream temperature TDEX at constant time intervals during the regeneration control. Also, the second DPF accumulation amount GDPF2 may be calculated according to the temperature accumulated value ITDEX.

Further, in the regeneration control, the downstream temperature TDEX may be detected at constant time intervals, the past value detected one sampling period before may be subtracted from the present value to calculate a temperature rising rate parameter DTDEX indicative of a rising rate of the downstream temperature TDEX, and the second DPF accumulation amount GDPF2 may be calculated according to the temperature rising rate parameter DTDEX.

The present invention can be applied also to an exhaust gas purifying apparatus for a watercraft propulsion engine, such as an outboard engine having a vertically extending crankshaft.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all modifications which come within the meaning and range of equivalency of the claims are, therefore, to be embraced therein. 

1. An exhaust gas purifying apparatus for an internal combustion engine having filtering means for trapping particulates in exhaust gases from said engine, the exhaust gas purifying apparatus comprising: first trapping amount calculating means for calculating a first particulate amount indicative of an amount of particulates to be trapped by said filtering means, according to an operating condition of said engine; second trapping amount calculating means for calculating a second particulate amount indicative of an amount of particulates trapped by said filtering means, according to a temperature of said filtering means when a filter regeneration of burning the particulates trapped by said filtering means is performed; and failure determining means for comparing the first particulate amount with the second particulate amount, and performing a failure determination of said filtering means according to a result of the comparison.
 2. The exhaust gas purifying apparatus according to claim 1, wherein said failure determining means calculates a particulate trapping rate of said filtering means according to a ratio of the first and second particulate amounts, and determines that said filtering means fails when the particulate trapping rate is less than or equal to a predetermined threshold value.
 3. The exhaust gas purifying apparatus according to claim 1, wherein said first trapping amount calculating means calculates the first particulate amount by calculating an amount of particulates emitted from said engine at constant time intervals according to the operating condition of said engine, and accumulating the emitted amount.
 4. The exhaust gas purifying apparatus according to claim 1, wherein the filter regeneration is performed by a post-injection for increasing an amount of fuel supplied to said engine, or naturally performed in a high load operating condition of said engine.
 5. An exhaust gas purifying method for an internal combustion engine having a filter for trapping particulates in exhaust gases from said engine, said exhaust gas purifying method comprising the steps: a) calculating a first particulate amount indicative of an amount of particulates to be trapped by said filter, according to an operating condition of said engine; b) calculating a second particulate amount indicative of an amount of particulates trapped by said filter, according to a temperature of said filter when a filter regeneration of burning the particulates trapped by said filter is performed; c) comparing the first particulate amount with the second particulate amount; and d) performing a failure determination of said filter according to a result of the comparison.
 6. The exhaust gas purifying method according to claim 5, wherein a particulate trapping rate of said filter is calculated according to a ratio of the first and second particulate amounts, and a determination is made that said filter fails when the particulate trapping rate is less than or equal to a predetermined threshold value.
 7. The exhaust gas purifying method according to claim 5, wherein the first particulate amount is calculated by calculating an amount of particulates emitted from said engine at constant time intervals according to the operating condition of said engine, and accumulating the emitted amount.
 8. The exhaust gas purifying method according to claim 5, wherein the filter regeneration is performed by a post-injection for increasing an amount of fuel supplied to said engine, or naturally performed in a high load operating condition of said engine.
 9. A computer program embodied on a computer-readable medium, for causing a computer to implement an exhaust gas purifying method for an internal combustion engine having a filter for trapping particulates in exhaust gases from said engine, said exhaust gas purifying method comprising the steps: a) calculating a first particulate amount indicative of an amount of particulates to be trapped by said filter, according to an operating condition of said engine; b) calculating a second particulate amount indicative of an amount of particulates trapped by said filter, according to a temperature of said filter when a filter regeneration of burning the particulates trapped by said filter is performed; c) comparing the first particulate amount with the second particulate amount; and d) performing a failure determination of said filter according to a result of the comparison.
 10. The computer program according to claim 9, wherein a particulate trapping rate of said filter is calculated according to a ratio of the first and second particulate amounts, and a determination is made that said filter fails when the particulate trapping rate is less than or equal to a predetermined threshold value.
 11. The computer program according to claim 9, wherein the first particulate amount is calculated by calculating an amount of particulates emitted from said engine at constant time intervals according to the operating condition of said engine, and accumulating the emitted amount.
 12. The computer program according to claim 9, wherein the filter regeneration is performed by a post-injection for increasing an amount of fuel supplied to said engine, or naturally performed in a high load operating condition of said engine. 